The present invention relates generally to an apparatus, assembly, and system for providing shielding against electromagnetic interference (EMI). In particular, the invention relates to an improved apparatus, assembly, and system that are particularly adapted for shielding a circuit card in an electronic enclosure against the negative consequences of EMI by expeditiously complying with industry accepted standards.
Electromagnetic compatibility (EMC) means that electric and electronic devices are compatible with similar devices in their vicinity in terms of shielding against EMI caused by the electromagnetic (EM) energy levels so that EMI does not adversely affect their operations. Because of the faster and more powerful computer systems evolving, EMI levels associated therewith are consequently changing and becoming relatively more difficult to satisfy. Manufacturers seek to achieve EMC to avoid malfunctioning of their systems and for gaining product acceptance. Towards this end, standards and requirements governing EMI have been and are becoming very common since they represent a way of insuring proper operation of electronic equipment. Manufacturers generally desire these standards since they tend to ensure that electronic devices do not interfere with their own operation or the operation of nearby electronic equipment. Furthermore, trade is facilitated by, for example, overcoming technical barriers to products.
Many electronic devices, such as computers, are made from a plurality of various electronic components, such as printed circuit boards. The printed circuit boards are typically electrically and mechanically connected to a backplane that is located within the housing. For example, peripheral component interface (PCI) circuit boards or cards are often used to connect computer peripheral devices to, for example, a computer motherboard. In the evolving computer field there is a continuing trend for size reduction of components and increases in their operating capabilities. Moreover, as the capabilities of the electronic devices have increased, the number of electronic components, such as PCI boards, required to be located within a computer has also generally increased. The reduced sizes of the electronic devices coupled with the increased number of electronic components located within the electronic devices has increased the need for improved EMI shielding. The improved shielding requirements present even more problems with PCI boards since the latter generally interface to external peripheral components and accordingly are associated with openings in the electronic housing. These openings are generally detrimental to the EMI requirements of the electronic devices.
One known approach for dealing with EMI issues in the context of a computer system using PCI cards is to employ the open industry PCI standards established by and available from the PCI-Special Interest Group (PCI-SIG). The standards available from this group cover several aspects of the PCI cards. For addressing some of these standards, it is well known in the field to use tailstock assemblies that form part of a PCI card assembly and function as an EMI barrier. The tailstock are electrically conductive and act to reduce these EMI issues adjacent the end of the cards that are typically adjacent openings in a computer""s chassis. The tailstocks not only provide desired EMI shielding characteristics, but enhance overall card rigidity, as well as a serve as a convenient installing mechanism. A typical PCI card tailstock includes a unitary bracket comprised of an elongated, flat metallic stamped element that is secured, as by appropriate fasteners, to a card end. Tailstocks are provided with spaced apertures allowing for passage and coupling of electrical connectors to the PCI card as well as for controlling EMI emissions.
However, in order to comply with relatively more recent and more rigorous specifications specified in relevant standards for PCI cards (e.g., PCI Local Bus specification version 2.2), it is now recommended that the tailstock be attached to a bottom surface of the card as opposed to the previously recommended top card surface. A reason for the change is that it forces repositioning of the attaching tab to the PCI card, whereby a tailstock notch or opening formed adjacent the tab bend that provides EMI exposure is better shielded. While the tab relocation technique provides an enhanced EMI barrier or shield at this area, there are nevertheless some potential negative tradeoffs when implemented. For example, the relocated tab creates potential tolerance issues for the fastener used for joining the card to the tailstock. In particular, relocation makes it relatively more difficult to retain threaded fasteners within a PCI specification""s bottom or backside form factor. This form factor is intended to restrict board components from exceeding it so as to thereby minimize potential costly physical damage to surrounding components in an electronic enclosure. Moreover, in order to comply with this newer specification, a manufacturer would have to use shorter and relatively more costly specially constructed threaded fasteners. However, the use of shorter and specially constructed fasteners would lead to additional potential problems in that the strength of the threaded attachment is diminished due to fewer engaged threads being employed, thereby compromising the overall structural integrity of the PCI cards as well as being relatively more expensive than conventionally used or so-called off-the-shelf fasteners. It will be appreciated, therefore, that without the ability to provide for effective and reliable EMI shielding for electronic devices, such a PCI cards, in a computer system, especially in the context of satisfying industry accepted standards, the true potential of providing reliable EMI shielding is less than otherwise desired. Accordingly, it would be highly desirable to provide for effective EMC integrity in such systems by providing EMI shielding for such cards which satisfy certain industry accepted standards, whereby such cards can be used in multiple brands of computer systems.
An aspect of the present invention is to provide an apparatus for providing EMC integrity through the provision of EMI shielding of a circuit card.
An aspect of the present invention is to provide an apparatus for enhancing EMC integrity by providing EMI shielding of a PCI card so as to expeditiously comply with industry standards governing EMI.
An aspect of the present invention is to provide an improved circuit card assembly of the type noted for use in an electronic system that effectively provides EMC integrity for the card assembly and system.
Still another aspect of the present invention is to provide an improved PCI card assembly for use in a computer system that effectively provides EMI shielding integrity for the PCI card assembly and system but, in addition, complies with industry accepted standards controlling PCI devices relative to EMI.
Still another aspect of the present invention is to provide an apparatus, assembly and system for providing EMI shielding that complies with industry standards in a low-cost and reliable manner.
In this regard, the present invention provides an apparatus comprising: a body providing EMI shielding and including an attaching portion extending therefrom, the attaching portion has a segment at a proximal end portion thereof which blocks an opening in the body for controlling EMI leakage and positions the attaching portion so that a fastener can fasten the attaching portion to a circuit card such that a first fastener end is engageable in juxtaposed relationship with a first card surface and a second fastener end terminates so as not to extend generally beyond a predetermined distance from a second card surface of the card.
In an illustrated embodiment, the circuit card is a PCI card and the predetermined distance is defined as a form factor dimension established by a PCI specification. In another illustrated embodiment, the proximal end segment is a folded portion that provides a hem which positions the attaching portion relative to the card without compromising EMI blocking of the opening by the proximal end segment.
A tailstock assembly or apparatus comprises an elongated body portion providing EMI shielding and includes an attaching portion extending laterally therefrom. The attaching portion has a segment at a proximal end portion thereof which blocks an opening in a bracket portion for controlling EMI and positions the attaching portion so that a fastener can fasten the attaching portion to the PCI card such that a first fastener end is engageable in juxtaposed relationship with a datum surface of a PCI card surface and a second fastener end terminates so as not to extend generally beyond a predetermined distance from the PCI card surface opposite the datum surface.
The present invention also includes a circuit card assembly for use in providing EMI shielding for a circuit card, the circuit card assembly comprising: a circuit card; a fastener; and, a shielding apparatus. The shielding apparatus comprises: a body providing EMI shielding and including an attaching portion extending therefrom. The attaching portion has a segment at a proximal end portion thereof which blocks an opening in the body for controlling EMI leakage and positions the attaching portion so that a fastener can fasten the attaching portion to a circuit card such that a first fastener end is engageable in juxtaposed relationship with a first card surface and a second fastener end terminates so as not to extend generally beyond a predetermined distance from a second card surface of the card.
Still another preferred embodiment is directed to a computer system comprising an enclosure, circuit card assembly, and a mounting structure for the circuit card assembly of the type noted above.